Meal timing dominates the lighting regimen as a synchronizer of the eosinophil rhythm in mice.

Mouse eosinophils undergo circadian fluctuation, and the phasing of the rhythm normally is synchronized to the environmental light-dark cycle if food always is available. This study was undertaken to determine whether or not the same rhythm could be synchronized to restricted feeding schedules. It was found that if food is available ad libitum for only short spans (in this case, 4 h during each 24 h period), the rhythm becomes synchronized to the feeding schedule. In addition, restricting food to certain 4 h spans causes the amplitude of the eosinophil rhythm to increase significantly over that of normal, light-dark synchronized animals. Not all rhythmic variables synchronize to restricted feeding schedules. Some remain synchronized to the light-dark cycle; the phasing of others seems to be the result of an interaction between both the light-dark cycle and the feeding schedule. These studies help dispel the popular misconception that all body functions react in the same manner to different synchronizers and emphasize that one must not generalize about the synchronizing effect of feeding or lighting.